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The allocation group is derived from ji->ixpxd, which is copied from the on-disk inode in copy_from_dinode(). A corrupted image can set di_ixpxd to an address that maps beyond the mounted bmap's db_numag. The existing code stores that unchecked result in signed char active_ag and then uses it to index db_active[]. For example, an AG value of 249 wraps to -7 before the atomic increment, causing a write before db_active and corrupting adjacent struct bmap state. Compute the AG in an unsigned type and reject values outside db_numag before storing active_ag or indexing db_active[]. dbMount() already validates db_numag <= MAXAG, so accepted values fit in active_ag and in the db_active[] array. Fixes: d31b53e3cd06 ("JFS: Don't save agno in the inode") Cc: stable@vger.kernel.org Assisted-by: Codex:gpt-5.5 Signed-off-by: Kyle Zeng --- Changes in v2: - Fix build issues. - Avoid unnecessary type casts. fs/jfs/file.c | 32 +++++++++++++++++++++++++++++--- 1 file changed, 29 insertions(+), 3 deletions(-) diff --git a/fs/jfs/file.c b/fs/jfs/file.c index 81556da507b9..d34a4e95a809 100644 --- a/fs/jfs/file.c +++ b/fs/jfs/file.c @@ -12,6 +12,7 @@ #include "jfs_incore.h" #include "jfs_inode.h" #include "jfs_dmap.h" +#include "jfs_superblock.h" #include "jfs_txnmgr.h" #include "jfs_xattr.h" #include "jfs_acl.h" @@ -38,6 +38,24 @@ int jfs_fsync(struct file *file, loff_t start, loff_t end, int datasync) return rc ? -EIO : 0; } +static int jfs_get_active_ag(struct inode *inode, int *agp) +{ + struct jfs_inode_info *ji = JFS_IP(inode); + struct jfs_sb_info *sbi = JFS_SBI(inode->i_sb); + struct bmap *bmap = sbi->bmap; + u64 ag = BLKTOAG(addressPXD(&ji->ixpxd), sbi); + + if (ag >= bmap->db_numag) { + jfs_error(inode->i_sb, + "inode %llu has invalid active ag %llu\n", + inode->i_ino, ag); + return -EIO; + } + + *agp = ag; + return 0; +} + static int jfs_open(struct inode *inode, struct file *file) { int rc; @@ -63,11 +82,18 @@ static int jfs_open(struct inode *inode, struct file *file) if (S_ISREG(inode->i_mode) && file->f_mode & FMODE_WRITE && (inode->i_size == 0)) { struct jfs_inode_info *ji = JFS_IP(inode); + struct bmap *bmap; + int active_ag; + + rc = jfs_get_active_ag(inode, &active_ag); + if (rc) + return rc; + spin_lock_irq(&ji->ag_lock); if (ji->active_ag == -1) { - struct jfs_sb_info *jfs_sb = JFS_SBI(inode->i_sb); - ji->active_ag = BLKTOAG(addressPXD(&ji->ixpxd), jfs_sb); - atomic_inc(&jfs_sb->bmap->db_active[ji->active_ag]); + bmap = JFS_SBI(inode->i_sb)->bmap; + ji->active_ag = active_ag; + atomic_inc(&bmap->db_active[active_ag]); } spin_unlock_irq(&ji->ag_lock); } -- 2.43.0